1. Field of the Invention
This invention relates to a clamp and gamma correction circuit, and an image display apparatus and an electronic machine utilizing the clamp and gamma correction circuit, wherein the level of a image signal is clamped to a clamp voltage before the image signal is subjected to gamma correction.
2. Description of Related Art
Conventionally, in a liquid-crystal display, the black level of an image signal is clamped to a predetermined clamp voltage to make the image signal compatible with an appropriate voltage for driving the liquid crystal. Since the T-V curve that represents the characteristic of the liquid crystal in the relationship of transmissivity (T) and applied voltage (V) is steep in its rate of change in the vicinity of the black level, the gradation of the liquid crystal is known to drop in the vicinity of the black level. For this reason, gamma correction is performed by amplifying the image signal with different amplification factors depending on the level of the image signal.
It is a conventional practice, to gamma correct the image signal through a gamma correction circuit prior to clamping the black level of the image signal to the clamp voltage through a clamp circuit. However, clamping prior to gamma correction improves image quality. Thus, when adjusting the clamp voltage to its appropriate level the gradation of the liquid-crystal panel drops in the vicinity of a black level.